Medicament delivery device

ABSTRACT

A medicament delivery device includes a housing having a longitudinal axis, a container holder, an axially movable plunger adapted to be displaced along the longitudinal axis into the container holder, and an energy accumulating member arranged inside the housing and adapted for displacing the plunger along the longitudinal axis. The plunger includes an outer plunger rod and an inner plunger rod arranged at least partially inside the outer plunger rod, the inner plunger rod being threadedly engaged with the outer plunger rod and manually rotatable to displace the inner plunger rod along the longitudinal axis into the container holder.

TECHNICAL FIELD

Embodiments disclosed herein relate to medicament delivery devices forthe administering of medicaments, in particular medicament deliverydevices providing a mixing of two medicament components, such as aliquid and a powder, or two liquids.

BACKGROUND

The present invention relates to medicament delivery devices such asautomatic injection devices for injecting liquid medicament with aneedle in a patient, or nebulisers for administering a medicament in theform of a mist to be inhaled into the lungs of a patient.

Auto-injectors, or pen-injectors have been on the market for many years.During recent years some medicaments have been developed to be injectedby patients themselves. Therefore, depending on the intended use andtype of medicament, there have also been developed injection deviceshaving a varying degree of automatic functions to facilitate theinjection of medicaments in a reliable and safe way for patients andeven for trained personnel; e.g. physicians and nurses.

WO 2012/173553 discloses an injection device comprising a housing and acontainer holder arranged within the housing. The container holder isconfigured for accommodating a medicament container having a needleattached to one end thereof and a stopper sealingly and slidablyarranged inside the medicament container at the other end thereof. Aplunger rod is arranged with a proximal end thereof contactable with thestopper. A first and a second energy accumulating member is arranged inthe interior of the housing of the injection device and adapted toaccumulate and store energy. A plunger drive means is slidably arrangedin relation to the plunger rod, is rotationally locked to the plungerrod, and is rotatable in relation to the housing. The plunger drivemeans is operationally associated with the first energy accumulatingmember. A container driver is arranged for being connectable to thecontainer holder and is threadedly connected to the plunger rod. Thecontainer driver is operationally associated with the second energyaccumulating member such that due to an output axial force from thesecond energy accumulating member, the container holder and the plungerrod are axially moveable in relation to the housing along apredetermined distance towards the proximal end of the injection devicefrom an initial locked position to a second position whereby a needlepenetration is performed. The plunger drive means is locked from beingrotated by the container driver. The plunger drive means is releasedsuch that due to an output torque from the first energy accumulatingmember, the plunger drive means is allowed to be rotated and the plungerrod is urged towards the proximal end of the injection device whereby aninjection is performed.

Some medicaments which are administered via medicament delivery devicescomprise two medicament components, which require mixing before beingadministered via a relevant medicament delivery device such as aninjection device or a nebuliser.

In the context of a piston rod drive system for a manually operable drugdelivery device, WO 2012/085208 discloses a piston rod drive systemcomprising a main body adapted for coupling with a reservoir. A useroperable activation element is operatively coupled with the main bodyand configured to move axially and rotationally relative to the mainbody between a first position and a second position to transfer asolvent from a rear chamber of a cartridge to a front chamber thereof. Apiston rod element is operatively coupled with the activation elementand the main body and configured to move axially and non-rotationallyrelative to the main body in response to the activation element beingmoved between the first position and the second position. The drugdelivery device as such does not lend itself to be automated.

There exists a need for a medicament delivery device, which provides fora mixing of two medicament components and an automatic delivery of themixed components.

SUMMARY

It is an objective to provide an automatic medicament delivery device,which provides for a mixing of two medicament components held in amedicament container.

According to an aspect, this is achieved by a medicament delivery devicecomprising:

a housing having a longitudinal axis extending between, and along, aproximal end portion and a distal end portion of the housing,

a container holder arranged in the housing at the proximal end portion,

an axially movable plunger adapted to be displaced along thelongitudinal axis into the container holder, and

an energy accumulating member arranged inside the housing, the energyaccumulating member being adapted for displacing the plunger along thelongitudinal axis towards the proximal end portion. The container holderis adapted to accommodate a medicament container adapted for attachmentof a medicament delivery member at one end portion of the medicamentcontainer and comprises a first piston sealingly and slidably arrangedinside an opposite end portion of the medicament container, and a secondpiston slidably arranged inside an intermediate portion of themedicament container. The plunger comprises an outer plunger rod, and aninner plunger rod arranged at least partially inside the outer plungerrod. The inner plunger rod is arranged in threaded engagement with theouter plunger rod. The inner plunger rod is manually rotatable todisplace the inner plunger rod along the longitudinal axis in adirection towards the proximal end portion into the container holder.

Since the inner plunger rod is arranged in threaded engagement with theouter plunger rod and the inner plunger rod is manually rotatable todisplace the inner plunger rod along the longitudinal axis in adirection towards the proximal end portion into the container holder,the inner plunger rod is adapted to displace the first piston and amixing of two medicament components in a relevant medicament containerheld in the container holder is achieved. As a result, the abovementioned objective is achieved.

The medicament delivery devices may be, for instance, be an injectiondevice for injecting medicament in fluid form, or a nebuliser foradministering a medicament in the form of a mist to be inhaled into thelungs. The medicament is at least partially administered and powered bythe energy accumulating member displacing the plunger. The medicamentdelivery member may comprise a needle as used in an injection device, ora nozzle as used in a nebuliser.

According to embodiments, the medicament delivery device may comprise anactuation rod extending at least partially inside the inner plunger rod.The actuation rod may be arranged in sliding engagement with the innerplunger rod, such that upon rotation of the actuation rod, the innerplunger rod may be rotated and slid along the longitudinal axis. Thus,the inner plunger rod, due to the threaded engagement with the outerplunger rod, may slide along the actuation rod, and the inner plungerrod may be displaced into the container holder upon rotation of theactuation rod.

According to embodiments, the actuation rod may comprise a knob arrangedoutside the housing at the distal end portion. In this manner a user mayeasily rotate the actuation rod by turning the knob.

According to embodiments, the actuation rod may be adapted to lose itssliding engagement with the inner plunger rod when the inner plunger rodis positioned in an end position towards the proximal end portion in theouter plunger rod. In this manner, displacement of the inner plunger rodmay stop when the inner plunger rod reaches the end position, even if auser should continue to rotate the actuation rod.

According to embodiments, the outer plunger rod may be adapted to engagewith the inner plunger rod when the inner plunger rod is positioned inan end position towards the proximal end portion. In this manner it maybe ensured that the inner plunger rod remains in a position towards theproximal end portion when the entire plunger is to be displaced towardsthe proximal end portion to administer a medicament from a relevantmedicament container in the container holder.

According to embodiments, the outer plunger rod may comprise at leastone resilient projection adapted to engage with a recess in the innerplunger rod when the inner plunger rod is positioned in the end positiontowards the proximal end portion. In this manner, the outer plunger rodmay engage with the inner plunger rod.

According to embodiments, the energy accumulating member may comprise atorsion spring for transferring stored energy into a rotational movementfor the displacement of the plunger along the longitudinal axis in adirection towards the proximal end portion. In this manner, a sufficientforce for administering a medicament may be provided within acomparatively small space. The torsion spring may, for instance, extendaround a portion of the plunger.

According to embodiments, the medicament delivery device may comprise afixed member arranged inside the housing. The fixed member may beprovided with a threaded inner surface, wherein the outer plunger rodmay comprise a threaded outer surface. The threaded inner surface of thefixed member may engage with the threaded outer surface of the outerplunger rod. A first end of the torsion spring may be connected to thehousing and a second end of the torsion spring may be connected to theouter plunger rod and may be releasably engaged with the housing. Inthis manner, the torque from the torsion spring may be transferred tothe plunger rod. Moreover, energy may be stored in the torsion springuntil the second end of the torsion spring is released from engagementwith the housing.

According to embodiments, the outer plunger rod may be engaged with thesecond end of the torsion spring via a drive member. The outer plungerrod may be slidably connected with the drive member for sliding movementof the outer plunger rod along the drive member and the longitudinalaxis. In this manner, the torque from the torsion spring may betransferred via the drive member to the plunger rod. The outer plungerrod will slide along the longitudinal direction at least partiallyinside the drive member while the drive member is rotated. The rotationof the outer plunger member will advance the entire plunger towards theproximal end portion as the threaded outer surface of the outer plungerrod is engaged with the threaded inner surface of the fixed member.

According to embodiment, the medicament delivery device may comprise alocking arrangement for releasably locking the torsion spring in anenergy storing position. In this manner, the locking arrangement may beactuated to release the torsion spring.

According to embodiments, the locking arrangement may comprise a firstmember connected to the torsion spring and a second member connected tothe housing, the second member being adapted to be in a releasableengagement with the first member. In his manner, a user may actuate thesecond member to release the first member in order to release thetorsion spring.

According to embodiments, the locking arrangement may comprise a thirdmember being threadedly connected with the actuation rod and slidablyarranged in relation to the housing, wherein the third member in ablocking position may be arranged in abutment with the second member,and wherein a rotation of the actuation rod may slide the third memberalong the longitudinal axis and out of the abutment with the secondmember. In this manner, an unintentional actuation of the second membermay be prevented before the mixing of two medicaments in a medicamentcontainer held in the container holder.

According to embodiments, the first member may comprise an opening andthe third member may comprise a projection, the projection extendingthrough the opening to achieve a releasable engagement between the thirdand first members. In this manner, an additional locking of the firstmember may be achieved.

According to embodiments, the rotation of the actuation rod may slidethe third member along the longitudinal axis and release the releasableengagement with the first member.

Further features of embodiments and advantages will become apparent whenstudying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of embodiments, including their particular features andadvantages, will be readily understood from the example embodimentsdiscussed in the following detailed description and the accompanyingdrawings, in which:

FIG. 1 illustrates a medicament delivery device according toembodiments,

FIG. 2 illustrates a cross section through the medicament deliverydevice illustrated in FIG. 1,

FIG. 3 illustrates parts of the medicament delivery device illustratedin FIGS. 1 and 2 in an exploded view,

FIG. 4 illustrates a cross section through the embodiments of themedicament delivery device of FIGS. 1-3, and

FIG. 5 illustrates a cross section through the embodiments of themedicament delivery device of FIGS. 1-4.

DETAILED DESCRIPTION

Aspects of example embodiments will now be described more fully. Likenumbers refer to like elements throughout. Well-known functions orconstructions will not necessarily be described in detail for brevityand/or clarity.

FIG. 1 illustrates a medicament delivery device 2 according toembodiments. In these embodiments, the medicament delivery device 2 isillustrated in the form of auto injector. The medicament delivery device2 comprises a housing 4 having a longitudinal axis 6 extending between,and along, a proximal end portion 8 and a distal end portion 10 of thehousing 4. A medicament delivery member in the form of a needle assemblyis arranged to be connected at the proximal end portion 8. A cover 12 isprovided at the proximal end portion 8.

FIG. 2 illustrates a cross section through the medicament deliverydevice 2 illustrated in FIG. 1. A container holder 14 is arranged in thehousing 4 at the proximal end portion 8. An axially movable plunger 16is adapted to be displaced along the longitudinal axis 6 into thecontainer holder 14. An energy accumulating member 18 is arranged insidethe housing 4.

The energy accumulating member 18 is adapted to displace the plunger 16along the longitudinal axis 6 towards the proximal end portion 8. Theenergy accumulating member 18 comprises a torsion spring 19 fortransferring stored energy into a rotational movement for the displacingof the plunger 16 along the longitudinal axis in a direction towards theproximal end portion 8. The displacement of the plunger 16 will befurther discussed with reference to FIGS. 3-5 below.

The container holder 14 is adapted to accommodate a medicament container20. The medicament container 20 is adapted for attachment of themedicament delivery member, comprising a needle at a first end portionof the medicament container 20 at the proximal end portion 8 of thehousing 4. The medicament container 20 comprises a first piston 24sealingly and slidably arranged inside an opposite end portion of themedicament container 20, and a second piston 26 slidably arranged insidean intermediate portion of the medicament container 20.

Such a medicament container 20 is adapted to contain two medicamentcomponents, one of which is stored in a first space 28 between the firstpiston 24 and the second piston 26. The other medicament component isstored in a second space 30 between the first end portion of themedicament container 20 and the second piston 26. The two medicamentcomponents require mixing before being administered to a patient.

The plunger 16 comprises an outer plunger rod 32 and an inner plungerrod 34 arranged at least partially inside the outer plunger rod 32. Theinner plunger rod 34 is arranged in threaded engagement with the outerplunger rod 32. The inner plunger rod 34 is manually rotatable todisplace the inner plunger rod 34 along the longitudinal axis 6 in adirection towards the proximal end portion 8 into the container holder14 and the medicament container 20 to displace the first piston 24towards the second piston 26. Thus, the medicament in the first space 28is transferred into the second space 30. For instance, 8-14 fullrevolutions of the inner plunger rod 34 may be required for the innerplunger rod 34 to extend into the medicament container 20 to such anextent that the first piston 24 abuts against the second piston 26.

An actuation rod 36 extends inside the inner plunger rod 34. Theactuation rod 36 is arranged in sliding engagement with the innerplunger rod 34, and it is via the actuation rod 36 that the innerplunger rod 34 is rotated. Accordingly, when the actuation rod 36 isrotated, the inner plunger rod 34 is rotated and due to the threadedengagement with the outer plunger rod 32, the inner plunger rod 34 isslid along the actuation rod 36 and the longitudinal axis 6. Duringrotation, the actuation rod 36 remains in the same position along thelongitudinal axis 6. The actuation rod 36 comprises a knob 38 arrangedoutside the housing 4 at the distal end portion 10 for a user to graspand rotate.

The medicament delivery device 2 comprises a locking arrangement 62 forreleasably locking the torsion spring 19 in an energy storing position.The locking arrangement comprises a first member 64 connected to thetorsion spring 19 and a second member 66 connected to the housing 4. Thesecond member 66 is adapted to be in a releasable engagement with thefirst member 64. In these embodiments, the first member 64 comprises adisc 68 provided with peripheral radial slots 70, see FIG. 3. The secondmember 66 comprises a button 72 arranged in the housing 4, see alsoFIG. 1. The button 72 comprises at least one protruding member 74adapted to fit into at least one of the radial slots 70.

FIG. 3 illustrates the plunger 16, the actuation rod 36, the energyaccumulating member 18, and part of the locking arrangement of the FIGS.1 and 2 embodiments in an exploded view.

The actuation rod 36 is provided with a slot 40 extending along theactuation rod 36. The inner plunger rod 34 on its inside is providedwith a protrusion 39 (see FIG. 4), which extends into the slot 40. Thus,the sliding engagement between the actuation rod 36 and the innerplunger rod 34 is achieved. The knob 38 is fixedly attached to theactuation rod 36 to form one rotatable unit with the actuation rod 36.

The inner plunger rod 34 is adapted to engage with the outer plunger rod32 when the inner plunger rod 34 is positioned in an end positiontowards the proximal end portion 8, see also FIG. 4. For this purpose,the outer plunger rod 32 comprises at least one resilient projection 42(see FIGS. 2 and 4) adapted to engage with a recess 44 in the innerplunger rod 34 when the inner plunger rod 34 is positioned in the endposition towards the proximal end portion 8.

In the following, reference is made to FIGS. 3 and 2. A fixed member 46is arranged inside the housing 4. The fixed member 46 is provided with athreaded inner surface 48. The outer plunger rod 32 comprises a threadedouter surface 50. The threaded inner surface 48 engages with thethreaded outer surface 50.

A first end 52 of the torsion spring 19 is connected to the housing 4and a second end 54 of the torsion spring 19 is connected to the outerplunger rod 32. The second end 54 is furthermore releasably engaged withthe housing 4. In these embodiments, the second end 54 is connected tothe outer plunger rod 32 via a drive member 56. Accordingly, the outerplunger rod 32 engages with the second end 54 of the torsion spring 19via the drive member 56. The outer plunger 32 is slidably connected withthe drive member 56 for sliding movement of the outer plunger rod 32along the drive member 56 and the longitudinal axis 6. Such a slidableconnection may for instance be achieved by an inner side of the drivemember 56 being provided with at least one ridge 58 extending along thelongitudinal axis 6 and an outer side of the outer plunger rod 32 beingprovided with at least one ridge recess 60 extending along thelongitudinal axis 6. The at least one ridge 58 fits slidably in the atleast one ridge recess 60.

Thus, when the second end 54 of the torsion spring 19 is released, thestored energy from the torsion spring 19 is transferred as a torque viathe drive member 56 to the outer plunger rod 32. The drive member 56 andthe outer plunger rod 32 will be rotated by the torsion spring 19. Whilerotating, seen in a direction along the longitudinal axis 6, the drivemember 56 remains stationary while the outer plunger rod 32, with itsthreaded outer surface 50 engaging with the threaded inner surface 48 ofthe fixed member 46, is moved towards the proximal end portion 8.

The first member 64, i.e. the disc 68 of the locking arrangement isconnected to the second end 54 of the torsion spring 19 via the drivemember 56. Thus, as long as the disc 68 is locked by the at least oneprotruding member 74 of the button 72 engaging with at least one of theslots 70, the torsion spring 19 remains in its energy storing position.Only upon actuation of the button 72, the disc 68 and the torsion spring19 are released.

The locking arrangement comprises a third member 76 being threadedlyconnected with the actuation rod 36 and slidably arranged in relation tothe housing. The third member 76 is connected with the actuation rod 36via a threaded member 78. The threaded member 78 is fixedly connected tothe actuation rod 36 such that when the knob 38 is rotated, the threadedmember 78 is rotated together with the actuation rod 36.

The first member 64, i.e. the disc 68 comprise one or more openings 80and the third member 76 comprise a projection 82.

Returning to FIG. 2, herein the medicament delivery device 2 isillustrated in an initial state with inner plunger rod 34 arranged in anend position towards the distal end portion 10, and the medicamentcontainer 20 with medicament components unmixed.

The third member 76 of the locking arrangement 62 is positioned in ablocking position in abutment with the second member 66. Thus, thesecond member 66 is prevented from being unintentionally actuated. Theprojection 82 extends through one of the openings in the first member 64to achieve a releasable engagement between the third and first members76, 64.

FIG. 4 illustrates a cross section through the embodiments of themedicament delivery device 2 of FIGS. 1-3. In FIG. 4, the medicamentdelivery device 2 is illustrated in an intermediate state with the innerplunger rod 34 displaced along the longitudinal axis 6 towards theproximal end portion 8 by a user having turned the knob 38, and themedicament container 20 with medicament components mixed in its secondspace 30.

In this intermediate state, the actuation rod 36 has lost its slidingengagement with the inner plunger rod 34. More specifically, the innerplunger rod 34 has been displaced to an end position towards theproximal end portion 8, and the protrusion 39 of the inner plunger rod34 has slid out of the slot of the actuation rod 36. Thus, any furtherrotation of the actuation rod 36 will no longer translate into movementof the inner plunger rod 34 along the longitudinal axis 6.

Compared to the medicament delivery device 2 illustrated in FIG. 2, theknob 38 and the actuation rod 36 have been rotated by a user. Thus, thefirst piston 24 has been displaced towards the second piston 26, and theresilient projection 42 of the outer plunger rod 32 has engaged with therecess of the inner plunger rod 34. The rotation of the actuation rod 36has also slid the third member 76 of the locking arrangement 62 alongthe longitudinal axis 6 and out of the abutment with the second member66. Moreover, the rotation of the actuation rod has slid the thirdmember 76 along the longitudinal axis 6 and release the releasableengagement with the first member 64, i.e. the projection 82 has beenslid out of the opening in the first member 64.

FIG. 5 illustrates a cross section through the embodiments of themedicament delivery device 2 of FIGS. 1-4. In FIG. 5, the medicamentdelivery device 2 is illustrated after injection of the medicament.

Compared to the intermediate state of the medicament delivery device 2illustrated in FIG. 4, the proximal end portion 8 of the housing 4 hasbeen pressed against a body of a patient to insert a needle (not shown)into the body, whereupon the cover 12 has been pushed into the housing4. The button 72 has been pushed to release the second end 54 of thetorsion spring 19 from its engagement with the housing 4. Whereupon theplunger 16 and the first and second pistons 24, 26 have been displacedby the torsion spring 19 further into the medicament container 20injecting the medicament via the needle into the patient. When themedicament delivery device 2 was removed from the body, the cover 12 waspushed out of the housing 4 by a spring 84.

This invention should not be construed as limited to the embodiments setforth herein. A person skilled in the art will realize that differentfeatures of the described embodiments may be combined to createembodiments other than those described herein, without departing fromthe scope of the present invention, as defined by the appended claims.It is also understood by those skilled in the art that the cover 12 isan optional feature, which may be omitted in alternative embodiments.Again, other embodiments may comprise an automatic needle penetrationfunction. In alternative embodiments, the releasable engagement betweenthe third and first members 76, 64 may be omitted. Embodimentsimplemented in a nebuliser, wherein the mixing of two medicamentcomponents is required before being administered, via a medicamentdelivery member comprising a nozzle, as a mist to be inhaled by apatient, are equally foreseen by the skilled person. Although theinvention has been described with reference to example embodiments, manydifferent alterations, modifications and the like will become apparentfor those skilled in the art. Therefore, it is to be understood that theforegoing is illustrative of various example embodiments and that theinvention is defined only the appended claims.

As used herein, the term “comprising” or “comprises” is open-ended, andincludes one or more stated features, elements, steps, components orfunctions but does not preclude the presence or addition of one or moreother features, elements, steps, components, functions or groupsthereof.

The invention claimed is:
 1. A medicament delivery device comprising: ahousing; an outer plunger rod having a first threaded engagement withthe housing; a torsion spring; an actuation rod comprising a slot thatis elongated parallel to a longitudinal axis of the housing; and aninner plunger rod comprising a protrusion configured to engage the slot,the inner plunger rod having a second threaded engagement with the outerplunger rod, wherein the actuation rod is rotatable to displace theinner plunger rod along the longitudinal axis via the second threadedengagement, thereby causing the protrusion to disengage the slot, andwherein the torsion spring is configured to drive the inner plunger rodand the outer plunger rod via the first threaded engagement proximallyalong the longitudinal axis relative to the actuation rod.
 2. Themedicament delivery device of claim 1, further comprising a firstpiston, a second piston, and a medicament container, wherein the outerplunger rod is adapted to engage the inner plunger rod to moveproximally in unison with the inner plunger rod when the inner plungerrod is positioned such that the first piston is in contact with thesecond piston.
 3. The medicament delivery device of claim 2, wherein theouter plunger rod comprises a resilient projection adapted to engage arecess in the inner plunger rod when the inner plunger rod is positionedsuch that the first piston is in contact with the second piston.
 4. Themedicament delivery device of claim 1, further comprising a fixed memberarranged inside the housing and provided with a threaded inner surface,wherein the outer plunger rod comprises a threaded outer surface thatengages the threaded inner surface of the fixed member, and wherein afirst end of the torsion spring is connected to the housing and a secondend of the torsion spring is connected to the outer plunger rod and isreleasably engaged with the housing.
 5. The medicament delivery deviceof claim 1, further comprising a first piston, a second piston, and amedicament container, wherein the actuation rod is adapted to lose itssliding engagement with the inner plunger rod when the inner plunger rodis positioned such that the first piston is in contact with the secondpiston.
 6. The medicament delivery device of claim 1, wherein theactuation rod is rotatable with respect to the inner plunger rod whenthe protrusion is disengaged from the slot.
 7. The medicament deliverydevice of claim 1, wherein the outer plunger rod is configured to engagethe inner plunger rod to move proximally in unison with the innerplunger rod when the protrusion is disengaged from the slot.
 8. Themedicament delivery device of claim 1, further comprising a first memberand a second member, the second member being adapted to be in areleasable engagement with the first member, the first member comprisinga disc provided with peripheral radial slots.
 9. The medicament deliverydevice of claim 1, the outer plunger rod further comprising a projectionand the inner plunger rod further comprising a recess, the projectionadapted to engage the recess when the protrusion is disengaged from theslot.
 10. The medicament delivery device of claim 1, further comprisinga drive member, the outer plunger rod being slidably connected with thedrive member to move along the drive member and the longitudinal axis.11. The medicament delivery device of claim 10, the torsion spring beingconfigured to transfer a torque via the drive member to the outerplunger rod.
 12. A medicament delivery device comprising: a housing; aknob arranged outside the housing; an outer plunger rod having a firstthreaded engagement with the housing; a torsion spring; an actuation rodcomprising a slot that is elongated parallel to a longitudinal axis ofthe housing; and an inner plunger rod comprising a protrusion configuredto engage the slot, the inner plunger rod having a second threadedengagement with the outer plunger rod, wherein the knob is rotatable todisplace the inner plunger rod along the longitudinal axis via thesecond threaded engagement, thereby causing the protrusion to disengagethe slot, and wherein the torsion spring is configured to drive theinner plunger rod and the outer plunger rod via the first threadedengagement proximally along the longitudinal axis relative to theactuation rod.
 13. The medicament delivery device of claim 12, furthercomprising a first piston, a second piston, and a medicament container,wherein the outer plunger rod is adapted to engage the inner plunger rodwhen the inner plunger rod is positioned such that the first piston isin contact with the second piston.
 14. The medicament delivery device ofclaim 13, wherein the outer plunger rod comprises a projection adaptedto engage a recess in the inner plunger rod when the inner plunger rodis positioned such that the first piston is in contact with the secondpiston.
 15. The medicament delivery device of claim 12, furthercomprising a fixed member arranged inside the housing and provided witha threaded inner surface, wherein the outer plunger rod comprises athreaded outer surface that engages the threaded inner surface of thefixed member, and wherein a first end of the torsion spring is connectedto the housing and a second end of the torsion spring is connected tothe outer plunger rod and is releasably engaged with the housing. 16.The medicament delivery device of claim 15, further comprising a lockingarrangement for releasably locking the torsion spring in anenergy-storing position.
 17. The medicament delivery device of claim 12,further comprising a first piston, a second piston, and a medicamentcontainer, wherein the actuation rod is adapted to lose its slidingengagement with the inner plunger rod when the inner plunger rod ispositioned such that the first piston is in contact with the secondpiston.
 18. A medicament delivery device comprising: a housing; an outerplunger rod; a torsion spring; an actuation rod comprising a slot thatis elongated parallel to a longitudinal axis of the housing; and aninner plunger rod comprising a protrusion configured to engage the slotand a threaded engagement with the outer plunger rod, wherein theactuation rod is rotatable to displace the inner plunger rod along thelongitudinal axis via the threaded engagement, thereby causing theprotrusion to disengage the slot, wherein the torsion spring isconfigured to drive the inner plunger rod and the outer plunger rodproximally along the longitudinal axis relative to the actuation rod.19. The medicament delivery device of claim 18, further comprising adrive member, the outer plunger rod being slidably connected with thedrive member to move along the drive member and the longitudinal axis.20. The medicament delivery device of claim 19, the torsion spring beingconfigured to transfer a torque via the drive member to the outerplunger rod.